Patent Application
20050224664
This application claims priority of the German patent application 10 2004 017 971.9 filed Apr. 12, 2004, which application is incorporated by reference herein.
The invention concerns a stand, in particular a stand for a surgical microscope, having one or more energy storage elements. “Energy storage elements” are understood in general to be elements that are suitable for absorbing an energy or force and delivering it again, or converting it into a different form of energy, in defined fashion. Relevant in this context are springs of mechanical, pneumatic, or hydraulic type or a combination of such types, or shock absorbers. Gas springs are primarily used in stand construction, in particular for surgical microscopes, but springs of the other aforementioned types are also implemented.
In order to achieve a maximally space-saving stand configuration, stands having energy storage elements dispense with a counterbalancing arm configured as a counterweight, or even a counterweight that is located opposite the horizontal support, but instead make use of the energy storage element, which takes over the lever function of the horizontal support, in particular under the load of the microscope. Gas springs used for this purpose as energy storage elements comprise a cylinder that is internally hollow and is divided by a piston into two pressure chambers. The piston is equipped with small holes (nozzles) through which pressure equalization can take place only in delayed (“cushioned”) fashion. Because the cylinder represents a closed pressure system, pressure equalization takes place until the pressures in the two pressure chambers are the same.
Conventional stands with gas-spring bracing have proven successful, but are used only in stands that exhibit moderately homogeneous movement. Different types of bracing, for example the balance-like weight/counterweight system, are used for stands that need to be used over a larger movement space and/or with more convenient movement guidance.
Conventional gas-spring support systems in stands are interchangeable depending on the load that is to be used, i.e. different gas springs are used for different loads. This is necessary because the working range of conventional gas springs has insufficient bandwidth. The bandwidth of the various weights of the surgical microscope, depending e.g. on accessories, must be distributed over gas springs of different strengths so that a balanced-out state of the stand can always be guaranteed. In other words: assuming, for example, a gas spring having a conventionally narrow working range, if the surgical microscope hung on the stand were one equipped with more accessories than provided for, and if it balanced out in a certain position and then departed from that balanced position, the horizontal support would then move automatically into different positions.
Conventional gas-spring-braced stands have the disadvantage that because of the so-called “cosine function” of the load lever effect of the microscope along its vertical movement arc, the bracing effect that is present differs as a function of the angular position of the horizontal support with respect to the vertical support. The (lever) force on the gas spring acting as the supporting lever is also greatest with the stand in the pivot position in which the load is located farthest away from the vertical support (the horizontal support and vertical support form a right angle).
EP-B1-433 426 describes a compensating apparatus, having a gas spring as the energy storage element, that encompasses an arc-shaped or kidney-shaped elongated guidance hole on the vertical support in which the proximal end of a piston rod is guided, while the cylinder constituting the distal end of the gas spring is secured pivotably on the horizontal support. (In the remainder of this Application, “proximal” means “toward the vertical support” and “distal” means “away from the vertical support, toward the unattached end of the horizontal support”.) This construction with an arc-shaped elongated guidance hole is theoretically intended to prevent the hysteresis of the gas spring from becoming disadvantageously perceptible. “Hysteresis” is understood in general to mean the dependence of the physical state of an object on previous states, based on a residual effect (remanence) after removal of the applied physical magnitude or force.
It has been found in practical use, however, that this configuration is disadvantageous in that the proximal end of the piston rod does not move continuously in the arc-shaped elongated guidance hole but instead, when used, jumps from one extreme position to the other in the manner of a toggle lever; for a user, this requires an additional movement across the jumping point in order to achieve readjustment of the support conditions in the arc-shaped elongated guidance hole.
It is thus the object of the invention to arrive at an improved system having energy-storage-element bracing, in particular gas-spring bracing, that is adjustable to different loads on the one hand so as thereby to eliminate the interchanging of different gas springs for different loads, and on the other hand in order to eliminate the disadvantageous cosine effect of the horizontal support under the load of the microscope, or reduce it sufficiently that it is no longer an annoyance. The toggle-lever jump effect is also to be eliminated. At the same time, the energy storage element must meet the typical requirements for a surgical microscope stand, i.e. the energy storage element must be capable of absorbing a counterbalancing force of approximately 2000 N. Conventionally, however, such high-rated energy storage elements exhibit a spring progression of approximately 18%.
These objects are achieved by the selection of an energy storage element having a defined and selected spring progression of, in novel fashion, less than 10%, preferably less than 9% (conventional gas springs have, on average, 11-60%), preferably accompanied by the highest possible energy absorption. The latter is preferably approximately 2000 N. The lowest possible spring progression value also guarantees a low hysteresis, which has an annoying effect specifically in the small movement ranges that are typical of a surgical application. In other words, according to the present invention the static friction, which plays a substantial role in the context of small movements of the horizontal support, is kept as low as possible (less than 60 N), while the dynamic friction, which plays a role in the context of larger movements of the horizontal support, can assume any arbitrary and relatively larger value. The reason is that the dynamic friction is of subordinate significance because large movements of the horizontal support are necessary only in the context of prepositioning operations, but not in the context of fine manipulation movements during surgical use.
Simultaneously or alternatively, these objects can be achieved by the fact that in novel fashion, instead of the conventional installation of the gas spring piston rod on the vertical support and of the gas spring cylinder on the horizontal support, it is the gas spring cylinder and not the gas spring piston rod that is articulated at the displaceable mounting point of the vertical support. The gas spring piston rod is thus, in novel fashion, preferably articulated as far out as possible at the distal end of the horizontal support. On the one hand this reduces the disadvantageous effect of the cosine function of the load, since the weight of the cylinder is shifted from the distal end of the horizontal support closer to the vertical support. An additional result is that a smaller annoying variable magnitude is present, which in novel fashion is no longer determined by a larger shiftable cylinder mass but instead by a smaller shiftable piston-rod mass. On the other hand, a gas spring of the greatest possible length exhibits better hysteresis properties (because of larger pressure chambers and, associated therewith, a lower potential pressure in the gas spring).
It is also preferred, for the sake of larger pressure chambers (so that the spring progression value is lower) and better hysteresis properties associated therewith, to select gas springs having the largest possible cylinder diameters.
A further preferred embodiment of a gas spring designed specifically for the desired applications has the smallest possible outside diameter for the piston rod. This design feature once again makes it possible to improve the hysteresis properties and, most of all, to lower the static friction, in particular the necessary “breakaway” force, at the cost of an increase in dynamic friction.
A further action that, according to the present invention, improves the gas spring is to bore out the nozzles in the piston. In conventional gas springs the diameter of these nozzles is in the range of tenths of a millimeter; in novel fashion, however, it is increased to no less than 2 mm, preferably 4 mm. Static friction is thereby minimized.
It is furthermore preferred for the horizontal support to have a longer protrusion than in the case of conventional stands (900 mm instead of 700 mm). Assuming pivot angles at the articulation point of the support gas spring that are kept small or at the same magnitude, this feature, results not only in a larger pivot range for the load (surgical microscope) in the vertical, but also a larger radius of action.
A preferred embodiment of a stand according to the present invention additionally comprises a displacement apparatus for the articulation point of the gas spring. This displacement apparatus can be, as known from the existing art, a threaded spindle having a carriage with a guide and a joint, which spindle is driven manually or in motorized fashion. Reference is explicitly made to the possibility of combining this Application with an invention filed simultaneously by the same Applicant, in which a bidirectionally acting displacement apparatus is disclosed that can also be utilized in the context of the stand disclosed here.
The horizontal support of a stand such as the one used for surgical microscopes is usually configured as a parallelogram support. Horizontal supports of single configuration are also, however, within the scope of the invention.
As already mentioned, the energy storage element can be a gas spring. Also conceivable in general, however, are pneumatic or hydraulic or even mechanical springs, or combinations thereof.
The invention is moreover not limited to a stand having only one energy storage element; stand solutions having two or more energy storage elements are also intended to fall within the scope of the disclosure of this Application, especially with regard to an improvement in hysteresis properties.
Further embodiments of the invention are shown in the Figures. The invention will be explained in more detail, symbolically and by way of example, with reference to the Figures. The Figures are described continuously and in overlapping fashion. Identical reference characters denote identical components; reference characters having different indices indicate similar or functionally identical components. In the drawings:
a-3c schematically depict the so-called “cosine effect” in three different positions; and
Gas spring 7 is arranged with a cylinder 12 at distal articulation point 10 and with a piston rod 11 at articulation point 9.
This stand arrangement furthermore comprises joints 3a-d and a microscope carrier 5. Horizontal support 4 pivots about pivot axis 13, and in turn describes a movement arc 14 in the context of vertical pivoting movements.
a-c schematically depict the lever effect as a function of various angles of the horizontal support with respect to the vertical support (the so-called “cosine effect”).
The Parts List is a constituent of the disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 017 971.9 | Apr 2004 | DE | national |
